Re: [Xen-devel] How does domU access PCI configure space?

[Kai Huang <mail.kai.huang@xxxxxxxxx>]

On Mon, Dec 26, 2011 at 4:54 PM, Jean Guyader <jean.guyader@xxxxxxxxx> wrote:
> On 26 December 2011 09:50, Kai Huang <mail.kai.huang@xxxxxxxxx> wrote:
>> On Mon, Dec 26, 2011 at 4:22 PM, Jean Guyader <jean.guyader@xxxxxxxxx> wrote:
>>> On 26 December 2011 07:02, Kai Huang <mail.kai.huang@xxxxxxxxx> wrote:
>>>> Hi,
>>>>
>>>> In my understanding, domU's PCI configure space access (ncluding
>>>> virtual device's and direct io's) is always trapped and emulated by
>>>> xen hypervisor. How did xen do it? Through exposing PCI configure
>>>> space area to domU as non-accessible memory? Where's the code to deal
>>>> of this? Thanks!
>>>>
>>>
>>> Config space access happen through the IO port cf8 and cfc.
>>> When a guest write to an io port that will cause a VMEXIT then xen will
>>> forward the io port request to qemu. cf8 and cfc are owned by the PCI
>>> BUS device model in qemu then this code will interpret the config
>>> space request and send it to the right pci device model (code
>>> qemu/i386-dm/helper2.c qemu/hw/pci.c)
>>>
>>> Jean
>>
>> IO port only works for PCI device, and in real system should only be
>> used during early boot phase. All PCIE devices must use MMIO mechanism
>> to access configure space.
>>
>> Are you saying currently xen/qemu only exports PIO mechanism to domU,
>> and does not support PCIE devices emulation/passthrough?
>>
>
> xen/qemu doesn't emulate a PCIE bus, it only has PCI support.
>
> Jean

Oh. Is there any plan, or code branch we are working on to support
PCIE bus in xen/qemu now?

-cody

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